The invention relates to an electric circuit for a system having an element which can operate intermittently, in particular for a hazard warning system of a motor vehicle. The circuit includes a control device, at least one element which is connected to a driver output of the control device and can be operated intermittently, an activation switch which engages in a control line for controlling device activation, and a monitoring lamp which, during the active intermittent mode of the element, is operated by the control device in a first, intermittent state, via a connection line for a monitoring-lamp control device, and during a non-activated mode of the element, the monitoring lamp is in a second operating state which is different from the first.
A circuit of this kind for a motor vehicle hazard warning system is provided, for example, in known Mercedes-Benz series produced vehicles. In this conventional hazard warning system circuit in which a so-called hazard warning switch serves as an activation switch, in the housing of which switch the hazard warning monitoring light is integrated, the monitoring light is continuously operated by the flasher unit as a control device via a separate short-circuit-proof output driver unit. This is done specifically so as to flash during the active flasher mode of the flasher lamp and during the inactive flasher mode according to the signal on a vehicle search light line which is fed to the flasher unit. Using this signal, in the inactive flasher lamp mode the monitoring light is operated in a dimmed continuously lit state when the external lights of the vehicle are switched on while the monitoring light remains switched off when the exterior lights of the vehicle are switched off. Both a ground line for the hazard warning monitoring light and a positive voltage supply for the switch itself are fed to the housing of the hazard warning switch in order to operate the flasher unit so as to activate the hazard warning mode.
A circuit for a flasher unit in which a hot wire switch acts as clock pulse generator and a monitoring lamp is provided in addition to the flasher lamps is known from German Patent Document DE 28 13 738 1A. Between the hot wire switch on the one hand and the lamps which are all connected to a terminal at a common ground potential on the other, a reed switch is arranged in such a way that the monitoring lamp is connected via the reed switch contact, and the flasher lamps are connected via a flasher switch and the exciter winding of the reed switch, to the switching tongue of a clock switch which is mechanically controlled by the hot wire switch.
There is therefore needed an electric circuit for a system of the above-mentioned type which permits the monitoring light to be operated in the desired operating modes with a low outlay in terms of circuit technology.
These needs are met according to the present invention which provides a circuit including a control device, at least one element which is connected to a driver output of the control device and can be operated intermittently, an activation switch which engages in a control line for control device activation, and a monitoring lamp which, during the active intermittent mode of the element, is operated by the control device in a first, intermittent state, via a connection line for a monitoring-lamp control device, and during a non-activated mode of the element, the monitoring lamp is in a second operating state which is different from the first. The connection line for the monitoring-lamp control device is connected on the control device-side to the driver output for the at least one element which can be operated intermittently. The activation switch is a multi-level switch which has at least two permanent switched positions and is looped with a first switching level (B) into the control line for the control device activation and with a second switching level (A) into the connection line for the monitoring-lamp control device. The intermittent mode of the element is activated in one of the switched positions of the activation switch via the first switching level and the switching disconnection of the connection line for the monitoring-lamp control device is cancelled synchronously therewith via the second switching level.
By virtue of the connection of the monitoring light to a driver output of the control device, the driver output being provided for the intermittently element, a separate output driver unit in the control device for the monitoring light is not required. The arrangement of the multi-level switch with at least two permanent switched positions as an activation switch permits an automatic, simultaneous switching over of the mode of operation for the monitoring light depending on whether an active, intermittent operation is requested or not.
In an advantageous embodiment of the invention, the monitoring light of the control device is arranged remotely in a housing cf the activation switch, i.e. in the case of a hazard warning system in the housing of the hazard warning activation switch.
A further embodiment of the present invention provides for the use of the novel circuit for a hazard warning system of a motor vehicle which has a dimmed vehicle search light line as part of its vekicie electrical system. Here, there is a provision for the flasher monitoring light to be electrically connected to the dimmed vehicle search light line when the hazard warning mode is not activated.
Other objects, advantages and novel features of the present inventicn will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.